A wealth of evidence has shown that wearing a face mask helps prevent people from spreading the virus that causes COVID, SARS-CoV-2, to others and from becoming sick themselves. But there has been less guidance from public health officials on what kind of masks provide the best protection.

Early on in the pandemic, the U.S. Centers for Disease Control and Prevention and the World Health Organization told the public not to wear N95 respirators, a type of mask that is made from high-tech synthetic fibers and provides a high level of protection against virus-laden airborne particles called aerosols. That was because there was then a shortage of such masks—and health care workers desperately needed them. At the same time, both agencies said there was little risk of aerosol transmission of SARS-CoV-2. They recommended cloth masks or other homemade face coverings that can stop some relatively large virus-carrying droplets even as it became clear that SARS-CoV-2 commonly spreads through aerosols—and as the supply of better-quality masks increased.

Read more...